This patch enables support for nl80211. In case the libnl-genl-3.0
library isn't found, it will fall back to Wext instead.
The library to use can also be manually set with the CMake option
WITH_LIBNL.
The Wireless-Extensions (WE or Wext) are deprecated and long replaced
by cfg80211.
Although Wext isn't used by WiFi drivers anymore, CFG80211_WEXT allows
old tools to communicate with modern drivers by providing a wrapper
API.
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